[Danke]

From the HK forums.

While a standard European-style leather sling is available for the MP5, in my opinion the H&K web multi-purpose carrying sling is far superior. For years this sling was an enigma to me, as the H&K manuals do not adequately describe its installation and use. But once you solve the mystery of its employment, few other slings will satisfy you. To correctly install the H&K sling onto an MP5, first attach the sling's spring-loaded hook into the eyelet on the front sight base. Then install the rear swivel by means of its spring-clip onto the buttstock. Pass the sling through the rear swivel and with its end-buckle connect it to the plain end of the second segment of webbing, which has a steel double-loop (with a diagonal bar) at the other end. Hang the double-loop on the spring-loaded hook attached to the front sight base. In this configuration you have a normal carrying sling.

To convert the sling into a "ready"- position carrying mode, pull the double-loop down and over the spring-loaded hook, and attach it to the spring-clip riveted to the left side of the magazine-well. Put the rear portion of the sling over your left shoulder and around your back. The front half will rest across your chest. With the buckle, adjust the sling until the weapon rests across your chest in a "port arms" position with the muzzle tilted upward. Grab the pistol grip and forearm and push the weapon sharply forward. The double-loop will snap out of the spring-clip on the magazine-well. Simultaneously bring the weapon up into the firing position onto your shoulder.